1. Field of the Invention
The present invention relates to a colored radiation-sensitive composition, a colored cured film, a color filter, a pattern forming method, a color filter production method, a solid-state image sensor, and a image display device which are suitable for producing a color filter used in a liquid crystal display device, a solid-state image sensor, and the like.
2. Description of the Related Art
As one of the methods of producing a color filter used for a liquid crystal display device or a solid-state image sensor, there is a pigment dispersion method. As the pigment dispersion method, there is a method of producing a color filter by photolithography by using a colored photosensitive composition that is obtained by dispersing pigments in various photosensitive compositions. That is, a curable composition is coated onto a substrate by using a spin coater, a roll coater, or the like, the substrate is dried to form a coating film, and the coating film is developed by pattern exposure, thereby obtaining colored pixels. This operation is repeated for the number of the desired colors to prepare a color filter.
Using pigments, the aforementioned method is stable with respect to light or heat, and positional accuracy is sufficiently secured since patterning is performed by photolithography. Accordingly, the method has been widely used as a method suitable for producing a color filter for color display or the like.
Meanwhile, in recent years, there has been a demand for color filters for a solid-state image sensor such as CCD to have high definition. As the definition of color filter is heightened, the size of a pattern tends to be miniaturized, but it is considered that the pigment dispersion method that has been widely used in the related art has a difficulty in further improving resolution while also miniaturizing the pattern size. One of the reasons is that coarse particles generated due to the aggregation of pigment particles cause color unevenness in a fine pattern. Consequently, in recent years, the pigment dispersion method having been widely used so far has not necessarily been used for purposes requiring a fine pattern, such as in a solid-state image sensor.
In the related art, a color filter has been prepared using a pigment as a colorant. However, today, use of a dye instead of a pigment is under examination. When a dye is used, the following points particularly become problems. (1) A dye is generally inferior to a pigment in terms of light fastness and heat resistance. Particularly, there is a problem in that optical characteristics are changed due to a high-temperature treatment performed at the time when a film is formed of indium tin oxide (ITO) which is widely used as an electrode of liquid crystal display or the like.
(2) Since a dye tends to suppress a radical polymerization reaction, in a system using radical polymerization as curing means, there is a difficulty in designing a colored photosensitive composition.
Particularly, when photolithography is used for preparing a color filter, the following points become problems.
(3) Generally, a dye exhibits low solubility in an aqueous alkaline solution or an organic solvent (hereinafter, simply referred to as a “solvent”), and accordingly, it is difficult to obtain a colored photosensitive composition having a desired spectrum.
(4) A dye interacts with other components in a colored photosensitive composition in many cases, and it is difficult to regulate the solubility (developability) of an exposed and unexposed portions.
(5) When a molar absorption coefficient (E) of a dye is low, the dye has to be added in a large amount. As a result, amounts of other components in a colored photosensitive composition, such as a polymerizable compound (monomer), a binder, and a photopolymerization initiator, have to be relatively reduced, and curability of the composition as well as heat resistance, developability, and the like of the cured composition deteriorate.
Due to these problems, it has been difficult so far to form a colored pattern that is constituted with a fine and thin film for a high-definition color filter and has excellent toughness by using a dye. Moreover, in a case of a color filter for a solid-state image sensor, a colored layer is required to be formed of a thin film of 1 μm or less. Accordingly, in order to obtain desired absorption, a relatively large amount of dye needs to be added to a curable composition, and consequently, the aforementioned problems arise.
Furthermore, it is known that when a colored photosensitive composition containing a dye is formed into a film and then subjected to a heating treatment, a phenomenon of color migration easily occurs between different colors of colored patterns adjacent to each other or between layers disposed and stacked on each other. In addition to color migration, there is also problems in that a pattern is easily peeled off in an area with a low exposure dose due to decrease in sensitivity; since the amount of photosensitive components contributing to photolithography characteristics is relatively reduced, an intended shape or color density is not obtained due to heat sagging (phenomenon in which a film is melted due to heating) or elution caused at the time of development; and the like.
As methods for resolving such problems, various methods, such as selecting the type of initiator and increasing the amount of initiator added, have been suggested in the related art (for example, see JP2005-316012A). Moreover, a color filter production method, in which a colored pattern is formed and then irradiated with light while a substrate is being heated so as to increase a polymerization rate of the system by performing polymerization at an increased exposure temperature, has been suggested (for example, see JP3309514B). In addition, a color filter production method, in which light irradiation is performed between a development treatment and a heating treatment so as to prevent deformation of a color filter, has been suggested (for example, see JP2006-258916A). Furthermore, a method of resolving the aforementioned problems by polymerizing a dye has been suggested (for example, see JP2007-139906A, JP2007-138051A, JP3736221B, and JP2000-162429A)